This invention generally relates to intake and exhaust valves of a vehicle engine. More particularly, the invention pertains to a variable valve timing control device for controlling the opening and closing timing of an intake valve and an exhaust valve of a vehicle engine.
A known variable valve timing control device is described in Japanese Patent Laid-Open Publication No. H09-324613. This disclosed variable valve timing control device is provided in connection with the drive train that transmits a driving force from a crankshaft of an engine to a camshaft for opening and closing an intake valve or an exhaust valve of the engine. The known variable valve timing control device includes a housing member unitarily rotated with the crankshaft and the camshaft and a rotor member assembled for relative rotation in the housing member for forming a hydraulic pressure chamber between the housing. A vane portion divides the hydraulic pressure chamber into an advanced angle hydraulic chamber and a retarded angle hydraulic chamber, and unitarily rotates with the camshaft and the crankshaft. The variable valve timing control device further includes a relative rotation control mechanism for restricting relative rotation between the housing member and the rotor member at an intermediate phase position (i.e., lock position) between a most advanced phase angle and a most retarded phase angle by a locking operation by virtue of the exhaust of an operation fluid and for allowing the relative rotation between the hosing member and the rotor member by an unlocking operation by virtue of supplying the operation fluid. The variable valve timing control device still further includes a hydraulic pressure circuit for controlling the supply and the discharge of the operation fluid to the advanced angle hydraulic chamber and the retarded angle hydraulic chamber, and for controlling the supply and the discharge of the operation fluid of the relative rotation control mechanism.
According to the aforementioned variable valve timing control device, the opening and closing timing (i.e., valve timing) of the intake valve or the exhaust valve is predetermined to achieve a preferable starting performance of the engine under the condition that the relative rotation between the housing member and the rotor member is restricted at the intermediate phase position between the most advanced angle phase position and the most retarded angle phase position by the relative rotation control mechanism. Thus, the starting performance of the engine may deteriorate in case the relative rotation control mechanism does not restrict the relative rotation between the housing member and the rotor member at the intermediate phase position upon the starting of the engine.
Factors associated with disturbing the restricting of the relative rotation between the housing member and the rotor member by the relative rotation control mechanism at the starting of the engine derive from the setting of the hydraulic pressure circuit and the residual operation fluid in the advanced angle hydraulic chamber and the retarded angle hydraulic chamber and the relative rotation control mechanism. According to known hydraulic pressure circuits, it is predetermined that the operation fluid is supplied to the advanced angle hydraulic chamber and to the retarded angle hydraulic chamber during the de-energization of a control valve provided in the hydraulic pressure circuit. In this type of hydraulic pressure circuit, the rotor member may not rotate relative to the housing member to be at the intermediate phase position by the supply of the operation fluid to the advanced angle hydraulic chamber or to the retarded angle hydraulic chamber when the control valve is under de-energization at starting of the engine.
A need thus exists for a variable valve timing control device which is not as susceptible to drawbacks mentioned above.
According to one aspect, a variable valve timing control device includes a housing member provided on a drive train for transmitting a driving force from a crankshaft of an internal combustion engine to a camshaft for opening and closing an intake valve and an exhaust valve of the internal combustion engine for being unitarily rotated with the crankshaft or the camshaft, and a rotor member relatively rotatably assembled in the housing member for forming a hydraulic pressure chamber with the housing member. The rotor member has a vane portion for dividing the hydraulic pressure chamber into an advanced angle hydraulic chamber and a retarded angle hydraulic chamber. The variable valve timing control device further includes a relative rotation control mechanism for allowing relative rotation between the housing member and the rotor member by performing an unlocking operation through supply of an operation fluid and for restricting relative rotation between the housing member and the rotor member at an intermediate phase position between a most advanced angle phase position and a most retarded angle phase position by the discharge of the operation fluid. A hydraulic pressure circuit controls the supply and discharge of the operation fluid of the advanced angle hydraulic chamber and the retarded angle hydraulic chamber, and controls the supply and discharge of the operation fluid of the relative rotation control mechanism. A control valve provided in the hydraulic pressure circuit discharges the operation fluid from the advanced angle hydraulic chamber and the retarded angle hydraulic chamber and from the relative rotation control mechanism. The control valve includes a variable electromagnetic spool valve having different exhaust opening widths at a both drain function region at which the operation fluid is discharged from the advanced angle hydraulic chamber and the retarded angle hydraulic chamber, and has a larger opening for a passage in communication with the retarded angle hydraulic chamber or the advanced angle hydraulic chamber whose volume is large at idling of the internal combustion engine.
According to another aspect, a variable valve timing control device includes a housing member provided on a drive train for transmitting a driving force from a crankshaft of an internal combustion engine to a camshaft for opening and closing an intake valve and an exhaust valve of the internal combustion engine for being unitarily rotated with the crankshaft or the camshaft, and a rotor member relatively rotatably assembled in the housing member to define with the housing member a hydraulic pressure chamber. The rotor member has a vane portion dividing the hydraulic pressure chamber into an advanced angle hydraulic chamber and a retarded angle hydraulic chamber. A relative rotation control mechanism permits relative rotation between the housing member and the rotor member by effecting an unlocking operation between the housing member and the rotor member through supply of operation fluid, and restricts relative rotation between the housing member and the rotor member at an intermediate phase position between a most advanced angle phase position and a most retarded angle phase position by effecting a locking operation between the housing member and the rotor member through discharge of operation fluid. A hydraulic pressure circuit controls the supply and discharge of the operation fluid with respect to the advanced angle hydraulic chamber and the retarded angle hydraulic chamber and controls the supply and discharge of the operation fluid with respect to the relative rotation control mechanism. An electromagnetic spool valve provided in the hydraulic pressure circuit includes a spool that is positioned during de-energization of the variable type electromagnetic spool valve at a position forming a both drain function region in which the operation fluid is discharged from the advanced angle hydraulic chamber and the retarded angle hydraulic chamber.
In accordance with another aspect, a variable valve timing control device includes a housing member provided on a drive train for transmitting a driving force from a crankshaft of an internal combustion engine to a camshaft for opening and closing an intake valve and an exhaust valve of the internal combustion engine for being unitarily rotated with the crankshaft or the camshaft, and a rotor member relatively rotatably assembled in the housing member to define with the housing member a hydraulic pressure chamber, with the rotor member having a vane portion dividing the hydraulic pressure chamber into an advanced angle hydraulic chamber and a retarded angle hydraulic chamber. A relative rotation control mechanism permits relative rotation between the housing member and the rotor member by effecting an unlocking operation between the housing member and the rotor member through supply of operation fluid, and restricts relative rotation between the housing member and the rotor member at an intermediate phase position between a most advanced angle phase position and a most retarded angle phase position by effecting a locking operation between the housing member and the rotor member through discharge of operation fluid. A hydraulic pressure circuit controls the supply and discharge of the operation fluid with respect to the advanced angle hydraulic chamber and the retarded angle hydraulic chamber, and also controls the supply and discharge of the operation fluid with respect to the relative rotation control mechanism. An electromagnetic spool valve is provided in the hydraulic pressure circuit and includes a spool moved in response to energization of the electromagnetic spool valve. The spool is movable to a maximum moved position during energization of the variable type electromagnetic spool valve, with the maximum moved position constituting a both drain function region at which the operation fluid is discharged from the advanced angle hydraulic chamber and the retarded angle hydraulic chamber. The spool is positioned during de-energization of the electromagnetic spool valve at a position constituting a supply-drain function region at which operation fluid is supplied to one of the advanced angle hydraulic chamber and the retarded angle hydraulic chamber, and is drained from the other of the advanced angle hydraulic chamber and the retarded angle hydraulic chamber.